A steady low hum is almost always a ground loop: two mains-powered devices at slightly different earth potentials, connected by an analogue cable whose screen now carries the difference.
The five-minute diagnosis
Unplug the analogue interconnects one at a time and listen after each. When the hum stops, the last cable you removed is carrying the loop. If the hum is present with nothing connected but mains, the device itself is the source.
The fixes, safest first
- Use an optical connection between the two devices if one exists. Toslink carries light and cannot carry the loop.
- Plug everything into the same mains outlet or extension, so every device shares one earth reference.
- Reroute the cable away from mains leads, and cross them at right angles where they must meet.
- A ground-loop isolator on the offending analogue link, as a last resort — it works and it also sits in the signal path.
What never to do
Lift the mains earth, or use an adapter that removes it. It will stop the hum and it removes a safety protection that exists for an unrelated and much more serious reason.
The one hum that is not a loop
A buzz that changes with the picture, or that follows a dimmer switch being used. That is interference rather than a loop, and it is fixed by separating the cables or by changing the lighting.
Questions people actually ask
Will a more expensive cable stop it?
No. A ground loop is a difference in earth potential between two devices, and it travels down the screen of any analogue interconnect regardless of price. The fix is to break the loop, not to improve the cable.
What is the safest fix?
An optical connection where one is available, because light cannot carry the loop. Never remove an earth connection from a mains plug to stop a hum — that is a safety earth, and it is there for a different reason entirely.
Last reviewed 4 September 2026